1. Technical Field
The present invention relates to a yellow ink composition used in an inkjet printing method, an inkset for inkjet printing that contains the yellow ink composition, an inkjet recording method, and recorded matter.
2. Related Art
In recent years, much attention has focused on the inkjet recording method. The inkjet recording method is a printing method where printing is performed by discharging an ink composition as small droplets, and these small droplets adhere to a recording medium such as paper or the like. This method has the characteristics of enabling high-speed printing of a high-resolution high quality image using a relatively inexpensive device. Furthermore, inkjet recording devices that use this method have wide acceptance in the market because of the excellent printing quality, low cost, relatively quiet operation, and excellent graphics capability. Of these devices, thermal (bubblejet (registered trademark)) and piezoelectric drop on demand printers in particular have been commercially successful, and are widely used as printers for personal computers at the office and home.
Furthermore, in recent years, printed matter has been obtained by forming a color image using an inkjet recording method that uses a plurality of color ink compositions. Generally, formation of a color image is performed using three colors, namely a yellow ink composition, a magenta ink composition, and a cyan ink composition, or if desired, using four colors by adding a black ink composition. Furthermore, color images are also formed using six colors with the addition of a light cyan ink composition and a light magenta ink composition to the aforementioned four colors, or using seven colors by also adding a dark yellow ink composition. Combinations of two or more of these ink compositions are referred to as an inkset.
The ink compositions which are used in forming the aforementioned color image are required to have good coloring properties for the individual color of each ink composition, as well as the capability to create favorable intermediate colors when a plurality of ink compositions are combined, and the recorded matter obtained thereby must not discolor when stored.
Furthermore, in recent years, continuous improvements have been made in the printhead, in the composition, recording method, and media in order to achieve “picture quality” printing using a color inkjet printer, and the picture quality obtained is similar to a photograph and at a level indistinguishable from a “silver chloride photograph”. On the other hand, efforts are underway to improve the storage properties of the images of recorded matter obtained using a color inkjet printer by improving the ink compositions and the media, and in particular the light fastness of the image has been improved to a practical level.
However, degradation of the image occurs not only because of the effect of light, but also because of oxidation due to oxidative gases existing in the environment such as ozone, and water (humidity) in the environment, and therefore discoloration and fading of the image will proceed. Therefore, in order to further increase the storage properties of the image on recorded matter, it is desirable that the light fastness of the image that is formed by the ink composition be improved, in addition to improving the ozone resistance and the humidity resistance. Therefore, various investigations have been performed in order to improve the light fastness, ozone resistance, and humidity resistance of the inkjet recorded matter (refer to JP-A-2005-15813).
In an inkset, if the light fastness and the like of a specific ink composition are noticeably inferior to the light fastness and the like of the other ink compositions, the color formed by that specific ink composition will fade and discolor faster than the other colors, and the color balance of the entire image will be poor. Therefore, an observer will be aware of the degradation in the picture quality of the image in a shorter period of time than they could be aware of fading of an image formed by only one ink composition. Therefore, with an inkset, in addition to improving the light fastness and the like of each of the ink compositions which form the inkset, preferably the level of the light fastness and the like of each of the ink compositions, or in other words the degradation speed and the fading speed of an image formed by each of the ink compositions due to light, ozone, and water will preferably be as similar as possible. In other words, the light fastness and the like of each of the ink compositions that make up the inkset should be excellent, and preferably the difference in the light fastness and the like of each ink compositions will be small.
When considering the use of a pigment as a colorant for the ink for inkjet recording, a pigment has excellent light fastness and water resistance, but on the other hand, the number of types of colorant that can be used will be less than with a dye. When actually used as an ink for inkjet recording, there is a need to sufficiently investigate the balance between light fastness and chromaticity. Furthermore, when used as an inkset, in addition to improving the light fastness and chromaticity of each of the ink compositions which compose the inkset, the balance between light fastness and chromaticity between the individual ink compositions which compose the inkset must also be considered.